The present invention lies in the field of electric lamps in which power to an electric bulb is controlled by touching the lamp. The invention particularly concerns a light bulb socket for use in such a lamp that encloses a touch-responsive electrical circuit for controlling the delivery of AC power to a light bulb held in the socket.
In the prior art, electric lamps have been provided with electronic circuits that control delivery of power to an electric lamp bulb in response to a user's touching the lamp or a conductive member mounted on the lamp.
Electronic circuits that respond to the touching of a lamp to control power delivered to a lamp bulb are well known and conventionally include electronic circuitry that provides, in response to touching a lamp or a conductive member, electronic signals that control the firing angle of a thyristor or other three-port power semiconductor. In such a circuit the thyristor is connected between a source of AC power, such as an electrical power cord, and the socket into which a light bulb is threaded. The circuit includes touch control circuitry which senses a change in capacitance, conductivity, or inductance that occurs when the lamp is touched by providing firing angle control signals to the thyristor. Touch-control circuitry conventionally includes multi-state circuitry that transitions from state to state under the control of a sequence of touch inputs. In such circuitry, each state causes an associated firing angle signal to be delivered to the thyristor. This provides the touch circuit with the ability to switch varying levels of power to the bulb by controlling the amount of power conducted by the thyristor. A lamp user is thereby enabled to select varying levels of illumination and to turn the lamp on and off.
In order to permit the conversion of lamps controlled by mechanical switches to provide touch-control of bulb illumination levels, conventional light socket structures have been adapted to receive a touch circuit. For example, a conventional socket structure includes an upper portion for receiving the threaded portion of an electric bulb. A closed lower portion houses a switch assembly to switch power to the bulb. The socket is converted to touch-control by housing the touch-control circuit in the lower closed portion of the socket. Then, the attachment of the conventional socket containing the touch circuit to a lamp mounting post completes the conversion of the lamp to incorporate the touch-control feature.
However, it is a difficult and lengthy task to convert a conventional socket to provide the space that is necessary to accommodate all of the physical features of a touch responsive circuit. For example, a touch-responsive circuit must include electronic elements for converting conventional domestic AC power to DC power for circuit operations; as is known, such conversion circuitry characteristically includes discrete semiconductor elements such as diodes and a large capacitor. Further, safety regulations require isolation of the touch circuitry from the lamp in order to eliminate the possibility of electric shock, with the isolation typically provided by another large capacitor. Finally, the power conversion and electronic signal switching taking place in the touch control circuit generate radio frequency interference that can affect the operation of nearby receivers such as radios. Suppression of such interference is accomplished by filtration circuitry having a significant size.
In sum, the volume required to accommodate touch circuitry is difficult, if not impossible, to provide by adaptation of a conventional socket; there is simply too little available space inside the socket assembly to comfortably accommodate a touch circuit.
Further, a conventional bulb socket assembly is not adapted for dissipating the heat generated in the controlled semiconductor element providing power to the bulb. The volume available to mount a touch circuit in a conventional socket is normally closed, thus preventing cooling by conduction. Moreover, since the socket assembly portion in which the touch control circuit may be located is used for providing a touch control input to the circuit, the power conducting element must be electrically isolated from it, thus reducing the socket's effectiveness as a heat sink.
Therefore, it is evident that there is a need for a touch control electric light socket assembly that will provide the space and operational features necessary for incorporating a touch-responsive electric circuit used to control the provision of power to a light bulb.